John Chapman, Engineering Fellow and CTO of Cisco System’s Cable Access Business Unit, is a pioneer in broadband communications, having helped to define and write the original DOCSIS (Data Over Cable Service Specification) spec — which spawned the cable modem marketplace, and, consequently, the broadband explosion we’re living in right now. He’s currently leading the development of the DOCSIS 3.1 specification, which promises substantial throughput and speed gains for residential broadband consumers. In this Q&A, originally posted on the Cable Congress blog “Interview with John Chapman”, he characterizes the highlights of DOCSIS 3.1, why it matters, and current events.
Q. What does DOCSIS 3.1 mean to cable-delivered broadband, as opposed to fiber?
Chapman: Service providers are often under scrutiny in terms of their competitiveness, against fiber-to-the-premise architectures. DOCSIS 3.1 will go a long way in assuaging those misperceptions. It can make that hybrid fiber-coax plant perform as well as fiber, at a fraction of the price of a fiber upgrade. DOCSIS 3.1 is all about getting more bang for the buck – it’s a higher performing, lower cost technology.
Q. What is the biggest change coming, in DOCSIS 3.1?
Chapman: It’s difficult to identify just one – there are many. In an over-arching sense, it’s a technology and product refresh for cable-delivered IP services. By that I mean it advances the progression to full-spectrum technology, which gives service providers the ability to stripe IP services across the entire cable spectrum, over time. And, it enables more bits per Hertz, on the wire – always good.
Q. Published reports indicate that DOCSIS 3.1 has the potential to create 50% bandwidth increases, in the downstream and upstream signal direction. What does that mean for capacity and speed?
Chapman: It means data rates as high as 10 Gbps in the downstream (home-facing) signal direction, and as high as 2 Gbps in the upstream (network facing) direction. The capacity angle is quite interesting, especially for the upstream path. DOCSIS 3.1 offers a way to widen that spectral range, to as high as 200 MHz. That’s a quadrupling. Now, it’s a matter of figuring out when, why and how one would do that. But generally speaking, DOCSIS 3.1 is a far-reaching value proposition.
Q. When people talk about DOCSIS 3.1, the term “OFDM” usually is somewhere nearby. What is OFDM?
Chapman: It’s a really cool technology that will allow us to shape the spectrum to fit the downstream, rather than the other way around. It’s cool because it’s infinitely configurable – tens of thousands of tiny, 25 kHz-wide carriers. Mobile carriers already use OFDM, but it’s new to cable providers. They traditionally use Quadrature Amplitude Modulation, or QAM. Our role as a vendor is to find a backwards-compatible way to augment a provider’s modulation portfolio with OFDM, without disaffecting the installed base of QAM.
Q. What’s the current status of DOCSIS 3.1?
Chapman: Well, we just sequestered ourselves in Denver for a most of a week – It’s a really high-energy group. I’d say we’re seeing the light at the end of the tunnel, in terms of having a completed 3.1 specification. Then we can all start building product. I think it’s safe to say that most vendors anticipate product in the marketplace in the 2015 timeframe.